I have an MBA. I started in an evening program 1 year after my BSME was completed and after having 1 year in the workforce. I did it to diversify my skills to open more career opportunities, thinking that I may want to leave engineering since at the time my industry was down and having a lot of layoffs. I finished the MBA 2 years later and stayed in my same job for 2 more years. I was itching to try something else to utilize some of the business stuff I learned in the MBA program. I did that for about 1.5 years, then returned to the tech side because I preferred it. I don't think a program like I went to was worth much for me because 1.) I've discovered I'm not that interested in management, beyond being a technical manager and those skills are gained through working, and 2.) programs like I went to are too generic. I believe if you quit your job and go to a top program full time, your degree will be worth more to you. Now, I did learn some good things in the program and think any time spent being educated is worthwhile, but I just don't think that MBA=added success like some people might think.
My recommendation would be to do all the other things that are pluses for advancement in your field first, i.e. PE license, field assignments, supervise/mentor others, etc. Wait until you're feeling like you aren't growing anymore, then try the MBA.